Apparatus for cage rolling and welding

ABSTRACT

A storage crib is provided for a roll of wire fabric which is fed beneath a shear, to a cage forming assembly which forms the fabric into a concrete pipe reinforcing cage in such a manner that it encircles a boom extending over the forming rollers. When a cage is formed, the boom can be elevated, thus extracting the formed cage from the forming apparatus. The cage is then conveyed down the boom to a welding conveyor by which it is conveyed on a beam past a welding apparatus. The welding apparatus engages and holds a pair of juxtaposed circumferential wires and then travels with the cage as the wires are welded together. Upon completion of the weld, the wires are disengaged and the welding apparatus travels in the opposite direction towards the next pair of juxtaposed circumferential wires. The beam is supported by a plurality of supports which can be disengaged from the beam such that the cage can travel past each support as it travels towards the egress end of the welding apparatus.

[451'Aug- 14,1973

United States Patent [191 Nordgren Primary Exminer-R. F. Staubly [54] APPARATUS FOR CAGE ROLLING AND WELDING [75 Inventor:

Assistant Examiner-Hugh D. Jaeger Alfred A Nordgnn Holland Mich. Attorney-Price, Heneveld, Huizenga & Cooper is fed beneath a shear end of the welding apparatus.

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l APPARATUS lFOR CAGE ROLLING AND WELDING CROSS REFERENCE TO RELATED APPLICATION This is a divisional application of parent application Ser. No. 55,071, filed July l5, 1970, now U.S. Pat. No. 3,678,971, and entitled APPARATUS AND METHOD FOR CAGE ROLLING AND WELDING.

BACKGROUND This invention relates to the manufacture of wire fabric reinforcing cages for use in the production of concrete pipe. These cages are comprised of a plurality of circumferential wires 18 joined by longitudinal wires I7 (FIG. 2). It encompasses all operations from the storage of a roll of wire fabric to the completion of welding the juxtaposed ends of the circumferential wires of the cage (FIG. 3). Thus, storing, shearing, forming, conveying and welding are all within the ambit of this invention.

Currently, most cage forming operations begin with a roll of wire fabric being suspended on a pipe. The fabric is pulled off the roll and sheared at a length sufficient to give the cage a desired circumference. The fabric is then fed, usually by hand, through a set of forming rollers. The cage so formed is then transferred by one or two men to a welding station. Frequently, this is accomplished through the use of an overhead conveyor which first has to be positioned above the cage, then has to be activated to lift the cage and finally has to be moved into position above the welding station. The cage is then clamped in such a manner that the juxtaposed ends of each circumferential are in approximate alignment such that an operator can manually weld them together. In this manner, one or two men can form and another can weld approximately 250 cages per day.

To the inventors knowledge, only one type of apparatus has been previously developed for automatically welding cages. This was developed by the inventor himself and is disclosed in U.S. Pat. No. 3,370,150. In this apparatus, a cage is placed on a welding station and is clamped in such a fashion that all of the juxtaposed ends of the circumferentials are clamped together simultaneously. A welder then moves across the stationary cage and automatically welds the juxtaposed ends. While this apparatus may be superior in some ways to a hand-welding operation, it does suffer from drawbacks which make it uneconomical for a concrete pipe producer to invest in the apparatus. First of all, it is extremely difficult to clamp all of the juxtaposed ends of the circumferential wires together simultaneously. Accordingly, too many juxtaposed ends are not welded together by the welding apparatus as it moves across the stationary cage and have to subsequently be welded by hand. Secondly. the apparatus is quite slow since it takes a rather lengthy period of time for the welding apparatus to move across the stationary cage. Thus, this welding apparatus has not met with any wide degree of commercial success.

Some operations do use storage apparatus which is more sophisticated than that outlined above. Fabric rolls are sometimes placed onto beds of support rollers with the fabric being held in place between stationary plates. ln such systems, the fabric may even be fed out of the storage bed into a shearing station-by a drive system. The sheared fabric is then fed into a set of pinch rollers which are driven by a separate driven means.

One of the drawbacks of this prior art system is that the stationary plates of the fabric crib cause the ends of the longitudinal wires to bend as the fabric is unrolled. The longitudinal wires are those which extend the width of the fabric roll and are so-called because these are the wires which extend lengthwise of a completed cage. Additionally, it is necessary with storage beds of this type to provide separate storage beds for fabric rolls of different widths. Finally, the above described operation suffers in that two separate drive systems are required, one for the crib feed system and one for the forming roller system. Thus, this operation, while more sophisticated than that originally described, is considerably more expensive and still suffers from a number of drawbacks.

The instant invention includes a means for forming wire fabric into a cage and a completely new and revolutionary means for welding the juxtaposed ends of the circumferential wires of the cage. Additionally, means are included for conveying the cage from the forming means past the welding means. The conveying means are positioned relative to the forming means such that the cage is formed in operable alignment with the conveying means permitting the conveying means, upon actuation thereof, to automatically engage the cage. The welding means includes a means for sensing a passing circumferential wire and initiating welding in response thereto whereby the cage is welded automatically as it passes the welding means.

Other additional and narrower aspects of the invention are numerous. As the cage is conveyed past the welder, it is supported by a beam which floats in effect on a plurality of supports. Each support can be selectively disengaged from the beam such that the cage can be moved past the disengaged support. Means are provided for elevating the position of the beam and the position of the welding means such that cages of different diameters can be welded.

The welding means itself is movable in the same direction as the conveying means but is biased towards movement in the opposite direction such that it moves with the cage while a pair of wires are being welded, but moves towards the next set of unwelded wires upon completion of the weld. The welding means also includes a means for sensing the presence of wire adjacent thereto, means movable into engagement with juxtaposed ends in response to the sensing for holding the juxtaposed wires together, and means for activating the welding means following engagement ofthe juxtaposed wires. In this manner, the wires are held tightly together while the welding operation is carried on.

The wire storage crib includes a pair of oppositely disposed circular retaining plates which are rotatably mounted such that they roll with the fabric roll as it is unwound. This prevents the ends of the wires from becoming deformed. At least one of the retainer plates is axially adjustable such that fabric rolls of different widths can be used. One of the crib rollers on the fabric roll includes a hand wheel which alleviates the task of feeding the wire fabric from the fabric roll into the drive rollers. Additionally, an auxiliary fabric roll supporting roller is provided which can be elevated into supporting engagementwith the fabric roll when it has diminished in size, and thereby prevent it from falling between stationary crib rollers.

The forming apparatus and the feed rollers on the storage crib are driven by a common drive source.

Clutch means are provided between the drive source and the feed rollers on the storage crib such that it can be disengaged after a length of fabric has been cut and is being formed. As fabric is formed on the forming rollers, it curves up over the pinch rollers which drive the fabric into the forming roller. In order to prevent it from going back through the pinch rollers, a receiving pan is provided which fIts snugly against the top pinch roller. This pan can be elevated as the fabric is first fed through the pinch rollers and can then be lowered once the feeding operation has been completed.

The various features of this invention make it possible for one man to replace four or five men in a standard operation. Thus, one man can shear, form and weld one cage every 60 seconds or less. During a normal operating day, he can produce as many as 480 to 500 cages. Furthermore, the cages so formed are of better quality than are normally produced in existing operations. The welds in the juxtaposed ends of the circumferentials are almost perfectly uniform. Furthermore, a good weld is assured by the holding means whereby the wires are held together during welding. Deformed longitudinal wires are almost completely I eliminated by the unique storage crib apparatus. These and other aspects of this invention make it one of the most significant contributions to this art in years.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a perspective view of the overall forming and welding apparatus of this invention;

FIG. 2 is a perspective view of a portion of acage which has just been rolled;

FIG. 3 is a fragmentary plan view of the overlapping portion of a cage showing the manner in which the ends of the circumferential wires are juxtaposed;

FIG. 4 is a schematic view of the various crib and forming rollers used in storing wire fabric and forming cages;

FIG. 5 is a fragmentary end view of the left end of forming apparatus 3 as it is viewed in FIG. l; I

FIG. 6 is a schematic view showing the chain and ratchet means for adjusting the height of the forming roller in forming means 3;

FIG. 7 is a side view of the ratchet adjusting assembly of FIG. 6 with the ratchet handle not being shown;

FIG. 8 is a perspective view of the right end of storage means l, shearing means 2 and forming means 3;

FIG. 9 is a slightly elevated perspective view of the welding assembly S;

FIG. l is a side elevation of a portion of welding assembly v FIG. 1l is a schematic of the conveying means of welding apparatus 5;

FIG. 12 is a cross section taken along XII-XII of FIG. 10, showing a support 120 moving into engage ment with a support plate l 13 in order to support beam 110 of welding apparatus 5;

FIG. 13 is a schematic showing the'interrelationship and nature of the upper welding conveyor wheels l32a .and the beam conveyor lll;

FIG. 14 is a schematic view showing the nature of the drive system for beam conveyor lll;

FIG. 15 is a perspective view of Welder-collaborator 170;

FIG. 16 is a side elevation of the key components of Welder-collaborator 170;

FIG. 17 is another side elevation of the components of FIG. 16 in which plate 185 has been driven to the right; I

FIG. 18 is a side perspective view of weldercollaborator with welding gun 171 removed;

FIG. 19 is a view of the same thing after drive plate 1'85 has been driven to the righ as in FIG. 17;

FIG. 20 is a schematic view showing the manner in which Welder-collaborator 170 travels on track 220;

FIG. 21 is a perspective view of an alternative assembly for conveying a formed cage from forming apparatus 3 to welding apparatus 5;

FIG. 22 is a cross section of the adjustment assembly for the retaining plates; v v

FIG. 23 is a schematic plan view of the drive assembly for the feed and forming rollers;

FIG. 24 is a schematic cross section taken along XXIV-XXIV of FIG. 10;

FIG. 25 is a bottom schematic view of welder collaborator PREFERRED EMBODIMENT Referring to FIG. 1, it can be lseen that this invention includes a fabric storage crib l, a shearing station 2, a forming station 3, a transfer assembly 4 which initiates conveying, a welding assembly 5 and a control unit 6. A roll of wire fabric 16 is shown in storage on storage crib l. It is withdrawn from storage` -crib '1 and passed beneath .the shear 2 and into former 3. At an appropriate length, the wire is cut by shearing station 2 and the cut fabric is formed into a circular or elliptical cage such asis shown in FIG. 2. It is then conveyed by transfer assembly 4 to the welding assembly 5 at which the juxtaposed ends of the circumferential wires are aligned in a manner such as is illustrated in FIG. 3 and welded.

FABRIC STORAGE CRIB, sIIEARINO STATION AND FORMING STATION Fabric crib 1 includes a support frame 10 which is comprised largely of steel beams and other conventionally used structural material (FIG. l). A pair of oppositely disposed retainer plates llare rotatably mounted on frame 10 for the purpose of holding fabric roll 16 in place and insuring that it is unrolled in a properly oriented manner. Each retaining plate ll is mounted on the end of a threaded shaft 12 which is threaded within an adjusting sleeve 13 (FIG. 22). Adjusting sleeve 13 is rotatably carried by pillow block bearings 15 and has a wheel 14 on the end thereof. As fabric 16 is unrolled, retaining plates l1 will tend to rotate thereby preventing the ends of the wire fabric from bending. As they rotate, threaded shaft 12 and adjusting sleeve 13 will rotate as a unit. However, if it is desired to adjust the plates 1l towards one another or away from one another, one can do so by rotating each of the adjusting wheels 14. The inertia of plate l1 is such that rotation of wheel 14 causes Shaft l2 to thread within adjusting sleeve 13.

FIG. 4 is a schematic view of the various rollers which facilitate the storage, shearing and forming of the wire fabric. Those rollers which are power driven are designated by arrows which show the direction in which the rollers rotate. A bumper roller 19 is mounted on frame 10 to facilitate Vthe loading of a roll of fabric 16 into position between plates ll. Crib rollers 20 and 22 are provided to support fabric roll 16 in position between plates 1l. These rollers extend generally from one plate 1l to the other and are tangential with the plates. A hand wheel 2l is provided on crib roller 20 n order to facilitate the initial feeding of fabric from roll 16 to drive rollers 26 and 27 which will thereafter act to remove fabric from roll 16.

The fabric is fed down beneath a take-off roller 25 into engagement with drive rollers 26 and 27. Take-off roller 25 merely helps prevent the end of the wire fabric from curving upwardly rather than feeding into the drive rollers 26 and 27. Drive roller 27 is spring loaded by spring 28 which biases it towards engagement with top drive roller 26. This combination of a top driven roller and a spring loaded, driven bottom roller is commonly called a set of pinch rollers. These grasp the fabric firmly in order to unroll it from crib l. Also, roller 27 expands downwardly as longitudinal wires 17 pass through the pinch rollers 26 and 27. All of the rollers are mounted on frame 10.

Because of the unique means by which wire can be fed through the use of hand wheel 21 to pinch rollers 26 and 27, a rather large distance must be left between crib rollers and 22. Accordingly, as the roll of fabric diminishes, there is a possibility that eventually it will fall down between crib rollers 20 and 22. In order to prevent this occurrence, the inventor has provided an auxiliary crib roller 23 which is mounted on a hydraulic cylinder 24 (in turn secured to frame l0) such that it can be elevated into a position tangential with circular retaining plates 11. So elevated, it merely acts as any other of the crib rollers. However, in order to facilitate the initial feeding of fabric into the pinch rollers 26 and 27, roller 23 can be lowered by means of cylinder 24 in order to get it out of the way.

As fabric is driven through pinch rollers 26 and 27, it engages a flattening roller 29, mounted on frame l0, which tends to ,flatten the roller curvature which the fabric has as a result of being stored in fabric roll 16. From thence the fabric passes beneath shear 2 and on into forming station 3. A measuring means 4S is positioned near shear 2 in order to measure the amount of fabric which has passed and to signal shear 2 to cut, once a desired length of fabric has passed. Measuring means 45 may operate either electrically or mechanically. For example, an electric eye may be provided to count the number of longitudinals which have passed. The shear 2 can be any conventional shearing apparatus known in the art. The type preferable is that which includes a clamping plate and a sloping knife mounted side by side. When the measuring means 45 indicates that a desired length has passed, shear 2 is automatically activated. The clamping plate comes down first and holds the fabric against a table above which the fabric passes. The sloping knife follows closely behind to cut the wire.

The rollers of forming station 3 are mounted to a supporting frame 30 which can be seen in FIG. l. Referring again to FIG. 4, these rollers include first a guide roller 3l which tends to hold the fabric up and guide it into a second set of drive or pinch rollers 33 and 34. Again, bottom pinch roller 34 is biased by s'pring 35 into engagement with top pinch roller 33. These pinch rollers drive the fabric into engagement with a forming roller 36 which causesthe fabric to bend up and around top pinch roller 33.

In order to prevent the end of the fabric from again entering pinch rollers 33 and 34, a receiving pan 37 is provided. It includes a roller guard portion which is curved according to the curvature of pinch roller 33 and which fits snugly thereagainst as the fabric is formed. It also includes a bottom portion extending upwardly from the bottom edge of the curved portion. Pan 37 is mounted on hydraulic cylinders (not shown) such that as fabric is first fed into the forming station 3 and into the pinch rollers 33 and 34, pan 37 can be elevated to the position shown in phantom in FIG. 4. Thus, it will not interfere with this feeding operation. Once the fabric cut by shearing'station 2 has been engaged by pinch rollers 33 and 34, pan 37 is again moved downwardly by its hydraulic cylinders in order to allow the cage to curve the maximum possible distance around top pinch roller 33. In this way the cages formed are more perfectly circular (or elliptical if the forming roller 39 is adjusted during forming) than would otherwise be the case.

In order to vary the diameter of the cage being rolled, forming roller 36 is adjustable by means of an adjustment assembly 40 (FIGS. 4, S and 6). Basically, each end of roller 36 is mounted on the end of a threaded post 4l which threads in a cogged nut'42. Referring to FIG. 5, it will be seen that nut 42 is rotatably carried between a pair of bearing plates43 which are rigidly secured to frame 30. A sprocket chain 44 is then wrapped around both nuts 42 and extends between them across the front of forming apparatus 3 as is shown in FIGS. 1 and 6. By moving chain 44, the two nuts 42 are rotated and threaded posts 41 thread upwardly or downwardly in nuts 42 to thereby evenly adjust the height of roller 36 at both of its ends.

A special ratchet assembly 50 is provided for moving chain 44 (FIGS. 6 and 7). Referring to FIG. 6, it can be seen that ratchet assembly S0 includes a ratchet gear 5l and a pair of wrap gears 52a and 52b which are provided to insure a complete wrap of chain 44 about ratchet gear 5l. A conventional ratchet handle 53 can be turned to thereby turn gear 5l and drive chain 44 around nuts 42. Referring to FIG. 7, it can be seen that the ratchet gear 5l and wrap gears 52a and S2b are mounted in three brackets, e.g., first bracket 54, second bracket 55 and third bracket 56. Each bracket comprises a rectangular steel frame. Wrap gear 52h is mounted at one end of bracket 54 and ratchet gear 51 is mounted at the other. The axle of wrap gear 52a extends through bracket 54 and is mounted in second bracket 55 such that first bracket 54 and second bracket 55 are in pivotal relationship to one another. The remaining wrap gear 52a is then mounted at the other end of second bracket 55 and its axle extends through bracket 55 and into engagement with bracket 56. In this manner, second bracket 55 and third bracket 56 are in pivotal relationship to one another. The chain wraps around wrap gear 52a, ratchet gear 5l and then wrap gear B2b. Inforder to adjust the tension of chain 44 around these gears, a tumbuckle 57 is provided between the free ends of first bracket 54 and second bracket 55. The entire ratchet assembly 50 is then mounted to frame 30 by bolting the end of third bracket 56 to frame 30.

DRIVE ASSEMBLY FOR STORAGE CRIB 1 AND FORMING STATION 3 lThe driven rollers of storage crib 1 and forming station 3 are driven by a common drive assembly 60 (FIG. 8). Six hydraulic motors 61 spaced hexagonally about a suitable drive gear 62a, drive a main drive shaft 62 (FIG. 8). Each motor 6l drives a pinion 61a which engages gear 62a. If any one motor 61 breaks down, the unit will not be shut down since the remaining five motors 61 will continue to drive shaft 62. Main drive shaft 62 drives a rear chain 63 through a clutch chain 64 and a gear transfer assembly 65. Transfer gears 65 comprise a pair of adjacent gears mounted on a common axle. One is driven by chain 64 while the othei transfers this motion to chain 63. Clutch chain 64 is driven by drive shaft 62 and itself drives transfer gears 6 5 whereby the drive of shaft 62 is transferred to rear drive chain 63 in a conventional manner. Drive shaft includes a clutch assembly 66 whereby drive shaft can be disengaged from clutch chain 64 in order that the rotation ofthe rollers of storage crib l can be stoipped. A schematic view of this drive is provided in FIG. 23. Front chain 67 is also driven by main drive shaft 62 but there is no necessity for a clutch therebetween.

The drive chains 63 and 67 drive a plurality of gears which in turn rotate the various driven rollers which have heretofore been discussed. In order to avoid confusion, the various gears which are connected to the ends of rollers for driving them have been designated v with the same number as has been given to the rollers along with the letter a. On the other hand, idler gears which do not themselves drive any rollers have been separately identified.

Referring to FIG. 8, it can be seen that rear drive chain 63 drives gear 29a of flattening roller 29, vand gears 33a and 34a which in turn rotate pinch rollers 33 and 34. Additionally, rear chain 63 is vwrapped around a spring biased idler gear 68. Idler gear 68 is mounted on a lever 68a which is pivotally mounted at one end to frame l0. The free end of lever 68a is spring loaded by spring 68h whose end is operably connected by rod 68e` to frame 10. It also rides over a small idler gear 65a, adjacent transfer gear 65 (FIG. 23).

Front drive chain 67 extends over gear 33a of top pinch roller 33, under gear 36a of forming roller 36, over an idler gear 69 (hidden), under an automatically adjustable idler gear 70, over gear 34a of bottom pinch roller 34, under a chain tensioning idler gear 75 and fnally over gear 31a of guide roller 31.

Idler gear 70 is automatically adjustable so that the height of forming roller 36 can be changed without necessitating dual gear adjustment, or in the alternative, changing the length of drive chain 67. Gear 70 is mounted on a floating lever 71, so-called because it in turn is pivotally mounted at its end to another lever 72. A coil spring 73 forces floating lever 71 downwardly in order to keep tension on drive chain 6.7. Lever 72 is pivotally mounted at its center to frame 30 and is pivotally connected at its opposite end to a bracket 74 which in turn is operably secured to threaded post 4l. Thus, a downward adjustment of post 36a causes lever 72 to pivot about its center pivotal mounting, thereby causing idler gear 70 to move upwardly. Conversely, an upwardadjustment of roller 36 automatically causes gear 70 to adjust downwardly.

Idler gear 75 is uniquely spring loaded so that it maintains an even tension en drive chain 67 as bottom pinch roller 34a is forced downwardly by the passage of a longitudinal wire through pinch rollers 33 and 34. Gear 75 is mounted approximately in the middle of a lever 76 which is pivotally mounted at one end to frame 30. At its other end. there is a horizontal flange 77 having a hole therein to slidably accommodate a threaded post 78 which is pivotally mounted to frame 30. A spring 79 is maintained between flange 77 and a compression nut 80 on post 78 such that lever 76 and idler gear 75 are biased downwardly. The extent to which the free end of lever 76 can move upwardly is limited by a stop nut 81 threaded on post 78 for engagement by flange 77.

TRANSFER UNIT Transfer junit 4 is a conveying unit which removes a formed cage from forming station 3 and conveys it to welding assembly 5. It is part of an overall conveying system which ultimately conveys a formed cage past a collaborator-Welder 170 (FIG. 1) where the juxtaposed ends of the circumferential wires 18 (FIG. 3) are welded together.

Transfer lunit 4 includes along boom 90 (FIG. l) which' is pivotally mounted at one end 90a to floating beam 110 of welding assembly 5. From thence it extends out over forming station 3 parallel to, and closely adjacent top pinch roller 33. The free end of boom is secured to a chain 92 which extends upwardly over a pulley in the top of an elevator tower 91. The end of chain 92 is connected to a winding motor 93 whereby the free end of boom 90 can be elevated, thus pivoting boom90 about its pivoted end 90a.

Because boom 90 is closely adjacent top pinch roller 33, a cage which is formed by forming roller 36 is bent up and around boom 90 as wellas around pinch roller 33. Once the cage is formed, boom 90 is elevated, removing the formed cage from forming station 3 and allowing it to slide down boom 90 to welding station 5. When boom 90 is then lowered, the formed cage comes to rest on a pair of roller pipes 94, one of which is mounted on either side of boom 90 (only one roller pipe 94 is visible in FIG. 1). Roller pipes 94 are rollably mounted on a pair of side rails 96 which extend from about twelve feet in front of welding assembly 5 on down to the rear end thereof. Pipes 94 are rollably mounted on side rails 96 in order that a formed cage can readily be rolled around until the juxtaposed ends of the circumferential wires are properly oriented at the top of beam 110. Finally, transfer assembly 4 is completed by a pair of funnel flanges movably mounted to the frame 100 of welding unit 5 on either side of beam near the front end thereof. These act to funnel a cage into welding assembly 5 in a proper orientation to be welded. 4

WELDING ASSEMBLY 5 Superstructure Referring to FIG. l, the structure of welding unit 5 includes a foundation or lower frame 100 and an elevator frame 102 mounted on top thereof. Foundation frame 100 includes four corner posts 100s to the top of which are mounted four hydraulic cylinders 101. Elevator frame 102 is rigidly secured to the moving pistons of cylinders 101 such that its elevation can be varied as is indicated in phantom in FIG. l. Elevator frame 102 includes a center longitudinal beam 103 (FIG. 9) secured thereto from which a plurality of brackets 104 depend downwardly to provide mounting means for various elements which are preferably elevatable with elevator frame 102.

Floating Beam Beam 110, which has been mentioned supra, provides support for a formed cage as it progresses past the Welder-collaborator 170 (FIG. l). Referring to FIG. 10, it can be seen that beam 110 includes a continuous belt-type conveyor l 1l which travels over a plurality of spring loaded idler wheels 112. The spring loaded mountings for these wheels have been designated 112a. Conveyor 111 acts both to support a cage as it iswelded and to aid in conveying it past the Weldercollaborator 170.

Beam 110 is referred to as a floating beam because it is supported by a plurality of beam supports 120 mounted on frame 100 which can be selectively disengaged from beam 110 in order to allow a cage to pass (FIG. 1l). There are 6 such supports 120 in all and they have been labeled 120a through 120f. Support 120a is actually located beneath boom 90 which is in effect a pivoted extension of beam 1 10. The only difference between support 120a and the remaining supports is that it is normally out of engagement with boom 90 whereas supports 120b through 120f are normally in engagement with beam 110.

Secured to beam 110 and its pivotal extension boom 90 are an equal number of downwardly depending brackets 114 having support plates 113 on the ends thereof (FIGS. 10 and 11). Each beam support 120 includes a forked top 121 (FIG. 12) which embraces support plate 1 13 on either side thereof. Support plate 113 includes a knife edge 1 16 which allows the support 120 a small amount of lateral leeway as it comes into engagement with plate 1 13. Located in the base of forked top 121 is a wheel 122 which is spring biased upwardly. This engages the bottom of plate 113 as support 120 moves into engagement therewith and thereby minimizes friction between the two during the engaging operation.

Each support 120 is pivotally mounted to a pivot mount 123 which in tum is rigidly secured to foundation frame 100 (FIG. 10). Extending downwardly from the pivot point at an angle to the upper portion of support 120 is a lever portion 124. The end of lever portion 124 is pivotally joined to a link 125 which in turn is pivotally joined to the piston rod 126 of a hydraulic cylinder 128. Hydraulic cylinder 128 is rigidly mounted to foundation frame 100 and piston rod 126 slides within a sleeve 127 which is also rigidly mounted to frame 100. Support 120a and support 120b are mounted to pivot in a direction opposite to the direction of travel of the cage as it is conveyed, as can be seen by reference to FIGS. 9 and 11. Supports 120e` through 120f are mounted to pivot in the direction of travel of the cage.

The height of beam 110 can be varied by changing the relative position of brackets 114 with respect to beam 110. Each bracket 114 includes three sets of mounting holes 115 (FIGS. 10 and 11). By using a different set of holes to bolt bracket 114 to beam 110, one

f can change the relative elevation of beam 110 with respect to the supports 120. Several different sets of mounting brackets 114 and depending plates 113 can be made available for increasing the variety of elevations which are available. In this manner, the elevation of beam 110 can be changed in accordance with the relative elevation selected for elevator frame 102 and its depending members.

While the forked tops 121 of supports 120 act to give beam 110 lateral stability, longitudinal stability is provided by three stabilizer bars 118 (FIG. l1). A stabilizer bar 111B is positioned near the front of beam 110 and is generally hidden in FIG. 11. Another is positioned approximately in the middle of beam and is visible in FIG. 11. The third is positioned on down beam 110. As can be seen by reference to the center stabilizer bar 118 whose assembly is visible in fig. l1, it is welded to the end of a piston 117a of a hydraulic cylinder 117. It is slidably carried in a sleeve 118a which is also of a square cross section. Both sleeve 118a and cylinder 117 are rigidly secured to downwardly depending mounting bracket 104. Each stabilizer bar 118 can be injected by cylinder 117 into engagement with a pair of fore and aft stop lugs 119 on beam 110. The tip of bar 118 is knife-shaped in a manner comparable to the leading edge of support plates 113 such that a certain amount of leeway is provided in order to facilitate the engaging operation. Stabilizing bar 118 can also be elevated out of engagement with stop lugs 119 such that a formed cage is free to pass along beam 110 without being stopped by stabilizer bar 118.

Welding Conveyors In addition to boom 90 which acts as a conveyor, there are three welding conveyors all of which aid in conveying a cage past Welder-collaborator 170. Upper conveyor (FIGS. l, 9 and 10) includes a frame 131 which is rigidly secured to a plurality of downwardly depending mounting brackets 104. Mounted thereon are a plurality of conveyor wheels 132a which are driven by a chain 133 which rides over drive gears 132, mounted on axles common to wheels 132e (FIG. 24) and over a plurality of idler gears 134. (FIG. l0). Chain 133 is driven by a drive transfer gear assembly 135 (Two gears on a common axle) which in turn is driven by chain 137 via drive gear 136 and its drive motor 138. Each conveyor wheel 132a comprises a wheel with teeth extending radially therefrom as is indicated in FIG. 13. The teeth of each wheel 132a act to grab the circumferential wires of the cage and thereby push it along. Thus, the top of a cage is sandwiched between conveyor wheels 132a (and their frame 131) and continuous conveyor belt 111 (FIGS. 10 and 13). Wheels 132a are geared to rotate slightly faster than belt 111 travels, such that the opposite ends of each circumferential wire of the cage are held in reasonable juxtaposition.

The drive system for conveyor wheels l32a, including chain 133, drive transfer gears 13S, chain 137, drive wheel 136 and motor 138, also serves as a drive source for beam conveyor 111 (FIG. 14). ln addition to its drive gear 132, the rear-most conveyor wheel 132a on frame 131 includes a drive gear 141 mounted on the opposite side from gear 132. A chain 142 is driven by gear 141 over idler 144, inverter idlers 145 and a drive transfer gear assembly 146, all of which are mounted on a clutch plate 143. Drive transfer gear assembly 146 is a pair of adjacent gears mounted on a common axle such that one gear is driven by chain 142 while the other acts as a drive for a conveyor drive chain 147. Conveyor drive chain 147 is wrapped over a pair of idlers 148 and a drive transfer gear 149 which is mounted on a common axle with the end-most gear 112 of beam conveyor 111.

Clutch plate 143 is so designated because it can be moved up or down, thus moving drive transfer gears 146 into or out of engagement with conveyor drive chain 147. Clutch plate 143 is welded to a stabilizer bar 118 such as have been previously described. However, its guide sleeve 118a includes a slot extending from top to bottom thereof in order to allow clutch plate 143 to move with bar 118.

Finally, a bottom conveyor 155 is mounted on foun dation support 100 in a position beneath beam 110, extending from a point near the front of beam 110 to a point at the rear thereof (FIGS. 9 and 1 1). It comprises a pair of parallel endless chains 156 wound on foreand-aft sprockets and driven by a motor 157 at the rear of welding station 5. The engagement of conveyor 155 with the bottom of a cage being moved along beam 110 acts to minimize the effect of friction between the cage and side rails 96. Additionally, conveyor 155 can be driven at two speeds by motor 157, a slower speed for conveying the cage past Welder-collaborator 170 and a faster speed for moving the cage from the end of upper conveyor 130 and beam conveyor 111 to the end of welding station 5. At this higher speed, conveyor 155 acts as an egress conveyor for a completely welded cage.

Gate Switches through 160t` (FIG. 11). Switches 160a, 160e and 160f are mounted directly to downwardly depending mounting flanges 104. The remaining switches 160b through 160d are mounted on a spacer bar 166 which in turn is rigidly mounted to frame 131 of upper conveyor 130. Bar 166 spaces them slightly from the surface of frame 131 in order to allow clearance for the drive action of chain 133.

Switch assembly 160a controls the disengagement and engagement of support 120b while switch assembly 160b controls the engagement and disengagement of support l20a with beam 90. The remaining switch assemblies 160C through 160f control supports 120C through 120f respectively in a manner which will be described subsequently.

Referring to switch 160e` on either FIG. 10 or 1l`, it can be seen that each switch 160 includes a limit switch 161 which is engaged by the end 163 of a lever 162 which is pivotally mounted at point 162a. Each lever 162 includes a central portion extending downwardly from its pivoted end at a steep angle across the path traveled by the top portion of a cage on beam 110. A so-called extension portion 165 then slopes gradually rearwardly (to the left in FIGS. and 1l). The relatively steep angle of the central portion of lever 162 insures swift activation of limit switch 161 when it is contacted by a traveling cage while the more gradually sloping extension portion 165 increases the distance over which the cage and lever 162 will remain in contact without substantially increasing the number of degrees through which the lever 162 must be pivoted.

Welder-Collaborator Welder-collaborator assembly 170 is so-called because it simultaneously holds (collaborates) and welds the juxtaposed ends of a circumferential wire 18. It includes a welding gun 1.71 (FIG. which is part of a conventional MEG welder assembly. Gas line 172 can be seen leading to gun 171. A Hobard 180 gun, model 377-226 has been found satisfactory. One assembly for controlling and supplying the gun which has been found particularly well adapted for use in this invention is that manufactured by Miller under the model designation DIP-IRIG- 10. The 250 amp supply source is designated by Miller as CP-250-TS, and the electronic timer for timing the weld cycle is designated by the manufacturer as 054-187. Welding wire is fed from a roll 173 mounted on the top of elevator frame 103 (FIG. 9) and extends down through a feed tube to the tip of welder gun 171.

The essence of the Welder-collaborator are the sensing plate 175, holding fork 180 and drive plate 185 shown in FIGS. 16 and 17. Sensing plate 175 includes a downwardly extending sensing nger 176 and an elongated diagonal slot 177. Via slot 177, plate is pivotally and slidably mounted on a stud 187 extending from the surface of drive plate 185. Holding fork 180 is mounted directly below drive plate and includes a pair of cams 182 which mate with a pair of cam openings 186 in drive plate 185. Additionally, holding fork 180 includes a pair of studs 183 extending from its surface to provide guidance in a manner which will subsequently be described. Depending downwardly from fork 180 are a pair of prongs 181 which form a generally V-shaped opening for engaging and holding a pair of juxtaposed ends of circumferential wire 18 in a manner indicated in FIG. 17.

Holding fork 180 and drive plate 185 are mounted for slidable movement between a back plate 190 and a front plate 191 (see FIG. 25) which are bolted together in side by side relationships as at bolts 192 (FIGS. 18 and 19). Front plate 191 includes a pair of vertical slots 194 which accommodate studs 183 on holding fork 180 and thereby limit holding fork -180 to vertical movement. A spring 195 extends from one of the studs 183 to a-stud mounted on front plate 191 and thereby biases holding fork 180 towards upward movement.

Sensing plate 175 is sandwiched for movement between drive plate 185 and a shim plate 199 on its back side and a bracket 197 and plate 197a on its front side. Shim plate 199, bracket 1 97 and plate 197a are all rigidly secured to back plate 190 by appropriate means. A spring 196 is joined to a stud 178 on the upper righthand portion of sensing plate 175 and to a stud on bracket 197. This biases sensing plate 175 towards movement downwardly and forwardly. Stud 178 slides against the diagonal edge of a slide plate 198 which also acts to sandwich sensing plate 175.

The forward or left-hand edge of sensing plate 175 is engaged by the inwardly extending flanged point 204 of a trigger 202. Trigger 202 is sandwiched between front plate 191 and a switch mounting plate 200 which is bolted at its bottom to front plate 191. Switch plate 200 includes an inwardly extending stud 201 (hidden) upon which trigger 202 is pivotally mounted. Trigger 202 includes an outwardly extending flange 203 which engages the top of a limit switch 206, mounted on switch plate 200, in the manner shown in FIG. 15. Trigger 202 is joined at its top by a spring 205 to front plate 191 such that trigger 202 is biased for pivotal movement towards engagement with sensing plate 175 and towards engagement with limit switch 206.

A hydraulic cylinder 208 is also mounted to front plate 191 (FIGS. 15, 18 and 19). It includes a rearwardly extending rod 209 to the end of which are rigidly secured a vertically oriented drive flange 210 and a horizontally oriented switching flange 211. Drive flange 210 is rigidly secured at its end to drive plate 185 (FIG. 25). Switching flange 21 1 extends beneath a limit switch 213 which is rigidly mounted to an upwardly extending bracket 214 which in turn is rigidly secured to front plate 191. A shim 21S is provided between bracket 214 and front plate 191 to provide clearance for cylinder 208. Switching flange 211 includes a contacting shim 212, the position of which can be adjusted along the length of switching flange 211 `and the function of which is to engage limit switch 213 when rod 209 is driven by cylinder 208 to the right.

A bracket 216, comparable to bracket 214, is rigidly secured to the right front side of Welder-collaborator 170 and a horizontal bracket 217 extends therebetween-to provide a mounting bracket for Welder gun 171 (FIGS. 15, 18 and 19). A threaded welder adjustment shaft 219 is rotatably mounted on a small bracket 2l9a near the bottom of bracket 216 (FIG. 18 and 19). The end of threaded shaft 219 is operably secured to the base of welder gun 171 in order to provide a means for adjusting the relative position of the tip of welder gun 171 (FIG. 15).

Welder-collaborator 170 is. mounted for movement along a track 220 (FIGS. 18, 19 and 20) which merely comprises a long steel bar which is secured to, but spaced from frame 131 (FIG. 20). One end of bar 220 is adjustably mounted in a slot 221 in frame 131 while the other end of track 220 is hingedly mounted through hinge 222 to frame 131. One can adjust the relative height of Welder-collaborator 170 by loosening the right end of track 220 in slot 221 and swinging it either forwardly or rearwardly on hinge 222.

Welder-collaborator 170 is rollably mounted on track 220 by means of front and rear rollers 225. Front roller 225 is rotatably mounted between bracket 214 and a rear bracket 218 which is comparable to bracket 214 and extends upwardly from rear plate 190. Similarly, rear roller 225 is rotatably mounted between bracket 216 and a second rear bracket 218. A third or bottom roller 226 is mounted on brackets 227 which are rigidly secured to bracket 216 and itsmatching rear bracket 218 (FIGS. 18 and 19). While rollers 225 engage the top of track 220, roller 226 engages its bottom.

While Welder-collaborator 170 is movable in either direction on track 220, it is biased to movement towards the front of welding station 5, i.e., in a direction opposite to that traveled by a cage moving on upper conveyor 130, beam conveyor 111 and bottom conveyor 155. To achieve this bias, a cable 230 extends from the rear of Welder-collaborator 170 (FIG. 20) under a pulley 231 on frame 131 and over a pair of pulleys 231e which are mounted on elevator frame 102. A large weight 232 is then connected to the end of cable 230. It includes a collar 233 which is capable of engaging a start limit switch 234 and a stop limit switch 235 positioned adjacent the vertical path traveled by weight 232. Limit switch 235 will stop all of the cage conveyors 130, 111 and 155, if Welder-collaborator 170 moves too far to the rear of track 220 (the right in FIG. 20). As Welder-collaborator 170 is then pulled back to the front of track 220, weight 232 will eventually contact start switch 234 which will again initiate operation of the cage conveyors.

Auxiliary Transfer Unit While the pivoted boom 90 described earlier provides an excellant means for removing a fonned cage from forming station 3 and transferring it to welding unit 5, a slightly more sophisticated transfer unit is disclosed in FIG. 21. This comprise a take-off boom assembly 250 and an ingress conveyor 260. Take-off boom assembly 250 includes a tubular boom 251 which extends out over forming station 3 in the same manner as would boom 90. Thus referring to FIG. 21, the forming means 3 would be positioned between boom tower 253 and ingress conveyor 260. Boom 251 is rigidly secured to and; extends from a motor unit 254. Motor unit 254 drives a conveyor chain 252 which extends through the interior of boom 251 and over the top thereof such that a cage can be conveyed along the length of boom 251. Motor unit 254 is mounted to travel vertically on a boom tower 253. An elevator chain 255 is secured to motor unit 254, passes up over pulleys at the top of tower 253 and down to a cylinder 256 to which it is secured. Activation of cylinder 256 thus changes the relative elevation of boom motor 254 and boom 252 as is indicated by the phantom lines for boom 251. As a conveyor is formed over boom 251, it is elevated so as to engage the cage and lift it off top pinch roller 33. Motion in conveyor chain 252 is then initiated to drive the cage off the end of boom 251 and onto ingress conveyor 260.

Ingress conveyor 260 includes a pair of top side rails 262 mounted toa frame 261. These act to support a formed cage on the conveyor. A kick plate 263 is slidably mounted on a pair of tracks 264 and can be moved forwardly or rearwardly by a drive chain 265. As kick plate 263 is moved forwardly, it engages the rear end of a formed cage and drives it down ingress conveyor 260 towards welding unit 5.

OPERATION Cage Forming The first step in forming cages is loading a roll of fabric 16 into storage crib 1. Bumper roller 19 is provided for facilitating this operation by causing the roll to align properly as it rolls over it and into place. Once in place, the new roll rests on crib rollers 20, 22 and 23 (see FIG. 4). The next step is feeding fabric from the new roll into the first set of pinch rollers 26 and 27. One can initiate a rotational motion in fabric roll 16 by turning hand wheel 21 on crib roller 20. The fabric begin to roll and the free end naturally tends to unwind. As is does so, it passes beneath take-off roller 25 which prevents it from bending back upwardly towards the rest of the roll. One continues rotating hand wheel 21 until the fabric engages driven pinch rollers 26 and 27.

At this point, pinch rollers 26 and 27 begin pulling the fabric from roll 16 and feeding it through shearing station 2. As longitudinal wires 17 pass between pinch rollers 26 and 27, pinch roller 27 expands downwardly against spring 28 in order to facilitate this passage. Tension on chain 63 is maintained by spring 68h to thereby force gear 68 to the right. as viewed in FIG. 8. A driven tiattening roller 29 tends to flatten the fabric and also insures that it will pass beneath shearing station 2 rather than into it.

The fabric then passes beneath shear 2 and over a driven guide roller 31 which acts to guide the fabric into the second set of pinch rollers 33 and 34. At this point, receiving pan 37 is in its elevated position as shown in phantom in FIG. 4 so as to not interfere with the feeding of fabric into pinch rollers 33 and 34. The

first set of pinch rollers 26 and 27 and the second set of pinch rollers 33 and 34 are sufficiently close tpgether that fabric will pass from the first set 26 and 27 into engagement with the second set 33 and 34 before it is necessary to cut the fabric to the desired length.

As longitudinals 17 pass between pinch rollers 33 and 34, pinch roller 34 expands downwardly against biased spring 35. Additionally, idler gear 75 springs downwardly through the action of spring 79 (FIG. 8) and idler gear 70 springs downwardly through the action of coiled spring 73. In this manner, proper tension is maintained on drive chain'67.

As fabric passes between pinch rollers 33 and 34, it engages forming roller 36 which bends the cage upwardly over pinch roller 33 in the manner indicated by the arrows in FIG. 4. In the meantime, measuring means 45 is measuring the length of fabric which is passing shear 2. When a desired length of fabric has passed for formingv a given cage, drive motors 61 are` through the greatest arc possible before it engages re-` ceiving pan 37 (FIG. 4). Once the completely formed cage is removed from top pinch roller 33, in a manner to be subsequently described, clutch 66 is re-engaged and drive chain 63 again begins to drive pinch rollers 26 and 27 in order to bring more fabric beneath shear 2.

The measuring apparatus 45 is set such that the fabric is sheared closely adjacnet a longitudinal wire as can be seen by reference to FIGS. 2 and 3. However, the longitudinal wire must not be cut or split during the cutting operation. This results in one end of each circumferential wire being firmly held down by a longitudinal and thereby makes it easier for the Weldercollaborator 170 to align and hold the juxtaposed ends together while they are being welded. Additionally, the American Society For Testing, And Materials, C76-68 Specification, specifies that for given cage diameters, there must be a certain amount of overhang, i.e., a certain lengh of overlapping circumferential wire extending beyond the first longitudinal 17. A minimum of 2 inches is required -where vthe wires are welded. This overhang" is indicated by the letter 0 in FIG. 3. If a minimum of 2 inch overhang is required and the spacing between adjacent longitudinals is 4 inches, then it is evident that if the cut were made 2 inches from each longitudinal, it would be difficult to obtain a proper amount of overhang.

ln order to change the diameter of the cage being formed, one merely changes the setting on measuring means 45 and changes the relative position of forming roller 36. This latter operation is performed by rotating ratchet lever 53 thereby causing chain 44 to travel and rotate adjusting nuts 42 (FIG. 6). This threads posts 41 either upwardly or downwardly and thereby varies the height of forming roller 36 (FIG. 5).

As the position of forming roller 36 is altered, its drive gear 36a will also move either upwardly or downwardly. In order to maintain proper tension on guide chain 67, the position of idler gear '70 is automatically adjusted in response to rotation of ratchet 53 (FIG. 8). Assuming forming roller 36 is moved downwardly,

bracket 74l which is operably connected to threaded post 41 is also moved downwardly thereby pivoting lever 72 about its central pivotal mounting. This moves lever 71 and idler gear 70 which is mounted thereto upwardly. Thus, the downward movement of drive gear 36a is oset by the upward movement of idler gear 70.

Cage Transfer Once a cage is formed over top pinch roller 33, it is ready for transfer to welding station 5. The operator of the apparatus stands adjacent control assembly 6 and calls for a cage by activating an appropriate control. This activates motor 93 on tower 91, thus elevating the free end of boom (FIG. l). The formed cage slides down boom 90 and boom 90 then settles back into its original position leaving the formed cage resting on roller pipes 94. Because support 120a. is normally disengaged from boom 90, it will not be in the way of the cage. By rolling, pipes 94 make it easy for the operator to rotate the cage until the juxtaposed ends of the circumferentials are positioned on top of beam 110. The operator 4then uses a small slotted gauge clamp to clamp together in spaced or guaged relation the two top adjacent longitudinalsv 17a and 17b (FIGS. 2 and 3). The clamp is applied near rthe rear end of the cage, i.e., the end towards forming station 3 and away from welding station 5. This holds the longitudinals 17a and 17b a given distance apart. The cage is now ready for conveyance past Welder-collaborator 170.

Cage Conveyance The operator now initiates cage conveyance by manually raising lever 162 of gate switch l60a (FIGS. 9 and 11). This causes support 120b to pivot downwardly in order to allow the cage to be passed into engagement with conveyors 130, 111 and 155. It also causes the first stabilizer bar 118 to move upwardly out of engagement with beam 110. From this point, the operation is entirely automatic. As the cage is passed into engagement with these conveyors, it is funneled through funnel flanges 95 which aid the gauging block in holding the cage in proper alignment. Once conveyance has begun, the operator removes the gauge block which he had previously placed on the rear end thereof.

As the cage is conveyed, the top longitudinals 17a and l7b, and the juxtaposed ends of the circumferentials are sandwiched between the conveyor wheels l32a and beam conveyor belt 111. Conveyor wheels 132a rotate slightly faster than conveyor lll travels in order to aid in holding the circumferentials in reasonable alignment. Friction between the bottom of the cage and side rails 96 on which it rests is minimized by the fact that the bottom of the cage is also being conveyed by conveyor 155.

As the cage is moved, it next engages and activates gate switch 160b (FIG. Il). This causes support l20a to move into engagement with support plate 113 of boom 90. Since the cage has now passed this point. there will be no interference between the engagement of support a and the cage. As lever 162 and its extention portion 165 of gate switch 160b is elevated. it engages the central portion of lever 162 on gate switch i.` (FIG. 11). Thus, gate switch160c is activated even before the cage actually reaches its lever 162. The

activation of gate switch 160e causes support 120e to 

1. A device for welding a pair of juxtaposed wires, said device and said juxtaposed wires being movable relative to one another, said device comprising: welding means for welding a pair of juxtaposed wires; holding means for holding the juxtaposed wires together; moving means for moving said holding means into and out of engagement with said juxtaposed wires; control means for controlling said welding means and said moving means, said control means operably interconnecting said welding means and said moving means, said control means being responsive to said moving means moving said holding means into engagement with a pair of juxtaposed wires whereby said welding means is activated by said control means in response to said moving means moving said holding means into engagement with a pair of juxtaposed wires; said control means being responsive to completion of welding of a pair of juxtaposed wires for activating said moving means whereby said holding means is moved out of engagement with said juxtaposed wires following completion of welding.
 2. The device of claim 1 which comprises: means for sensing the presence of wire adjacent said welding means, said holding means being movable into engagement with the juxtaposed wires in response to the sensing of wire by said sensing means.
 3. The apparatus of claim 1 in which said holding means defines a generally V-shaped opening which embraces said juxtaposed wires when said holding means is in engagement therewith.
 4. The device of claim 2 in which said sensing means comprises a switch and a movably mounted finger which projects beyond said welding means and is engaged by wire as it passes; said finger being moved by said wire to thereby activate said switch; means being activated by said switch for moving said holding means into engagement with said juxtaposed wires and for moving said finger out of the path of said juxtaposed wires; said moving means being deactivated following the welding of said juxtaposed wires to thereby move said holding means out of engagement with said wires and move said finger past the wires which have just been welded and into the path of the next set of unwelded juxtaposed wires.
 5. The device of claim 4 in which said control means includes a second switch which is activated by said moving means when said moving means is activated, said second switch controlling said welding means whereby welding is initiated when said second switch is activated.
 6. A device for welding a pair of juxtaposed wires moving with respect to the welding device, said device comprising: a welder; drive means; a sensing finger being pivotally and slidably mounted on said drive means and projecting beyond said welder into the path of said moving wires; a first switch activatable by said sensing finger as it is pivoted; moving means moving said drive means in response to the activation of said first switch; guide means guiding said sensing finger upwardly out of the path of said moving wires in response to the movement of said drive means; a holding fork being operably associated with said drive means; means guiding said holding fork downwardly in response to movement of said drive means; embracing means on said holding fork defining a generally V-shaped opEning for embracing and holding said juxtaposed wires adjacent said welder; a second switch being activatable by said moving means, said welder being activated in response to activation of said second switch.
 7. The device of claim 6 in which said drive means comprises a drive plate mounted for generally horizontal movement and including cam engaging surfaces thereon; said holding fork being mounted for generally vertical movement and including cams thereon engaging said cam engaging surfaces of said drive plate whereby when said moving means moves said drive plate in response to activation of said first switch, said holding fork is driven generally vertically downwardly by said cam engaging surfaces acting on said cams.
 8. The device of claim 7 in which said guide means for said sensing finger includes a generally diagonal slot in said sensing finger; a pivot stud being mounted on said drive plate and extending into said generally diagonal slot; means for limiting the horizontal movement of said sensing finger to an amount which is less than the extent to which said drive plate can be moved horizontally whereby when said moving means moves said drive plate in response to activation of said first switch, said sensing finger is moved upwardly out of the path of said moving wires by the limiting action of said means limiting the horizontal movement of said sensing finger and by the guiding action of said pivot stud in said generally diagonal slot.
 9. The device of claim 8 in which said limiting means comprises a slide plate having a diagonal edge engaging a corresponding edge on said sensing finger, said slide plate, said sensing finger, said drive plate and said holding fork being mounted in sandwich fashion between fore-and-aft mounting plates; said slide plate and said sensing finger being mounted in generally the same plane and said drive plate and said holding fork being mounted in generally the same plane, and being mounted to one side of said slide plate and said sensing finger.
 10. The apparatus of claim 8 in which said cam engaging surfaces on said drive plate comprise notched openings generally in the bottom of said drive plate and said cams on said holding fork comprise a projection upwardly generally into said notch openings. 